Bipolar power semiconductor components, like power diodes, power IGBTs (insulated gate bipolar transistors), or power thyristors, include a first emitter region of a first conductivity type, a second emitter of a second conductivity type, and a base or drift region of the first or second conductivity type arranged between the first and second emitter regions. The base region has a lower doping concentration than the first and second emitter regions. When the component is in a conducting state or on-state, charge carriers of the first conductivity type are injected into the base region from the first emitter region, and charge carriers of the second conductivity type are injected into the base region from the second emitter region. These charge carriers form a charge carrier plasma in the base region. This plasma with charge carriers of the first and second conductivity type results in a low resistance of the component in the on-state.
A diode, for example, is in the on-state when there is a voltage that causes the diode to be forward-biased, and a diode is in the off-state when the voltage causes the diode to be reverse-biased. During a transition from the forward-biased state to the reverse-biased state, which is when the diode transitions from the on-state to the off-state, these charge carriers forming the charge carrier plasma are removed from the base region. This is known as reverse recovery. During reverse recovery a reverse recovery current flows through the component caused by the removal of charge carriers from the base region. This current finally drops to zero as the charge carriers have been removed. A slope of this reverse recovery as it tends to zero defines the softness of the component. The steeper the slope, the less “soft” is the reverse recovery behaviour of the diode. A soft behaviour is desirable in that steep slopes cause voltage overshoots in parasitic inductances connected to the component and/or cause oscillations or ringing.